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Friday, 9 October

JEE Main 2020 · PhysicsMultiple choiceSingle correctMediumMulti-step

JEE Main 9 January 2020, Shift 2, Physics Q3

Question 3 of 75 in this shift, Physics question 3 of 25, Section A.

A uniformly thick wheel with moment of inertia II and radius RR is free to rotate about its centre of mass (see fig). A massless string is wrapped over its rim and two blocks of masses m1m_1 and m2m_2 (m1>m2m_1 > m_2) are attached to the ends of the string. The system is released from rest. The angular speed of the wheel when m1m_1 descents by a distance hh is :

The figure, in words

A wheel hung from a ceiling support; a string over its rim carries block m1 on the left (lower) and block m2 on the right (higher).
  1. (1)[2(m1+m2)gh(m1+m2)R2+I]12\left[\frac{2(m_1+m_2)gh}{(m_1+m_2)R^2+I}\right]^{\frac{1}{2}}
  2. (2)[2(m1−m2)gh(m1+m2)R2+I]12\left[\frac{2(m_1-m_2)gh}{(m_1+m_2)R^2+I}\right]^{\frac{1}{2}}Official answer
  3. (3)[(m1−m2)(m1+m2)R2+I]12gh\left[\frac{(m_1-m_2)}{(m_1+m_2)R^2+I}\right]^{\frac{1}{2}}gh
  4. (4)[m1+m2(m1+m2)R2+I]12gh\left[\frac{m_1+m_2}{(m_1+m_2)R^2+I}\right]^{\frac{1}{2}}gh

Official answer

Option 2

NTA final key (Jan 2020).

Chapter
System of Particles and Rotational Motion
Topic
Torque and Equilibrium
Idea tested
Torque of Tension on Pulleys

Same topic in other shifts

All Torque and Equilibrium questions
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  5. 9 Apr 2024, Shift 1 · Q33A heavy iron bar, of weight W is having its one end on the ground and the other on the shoulder of a person. The bar makes an angle…EasySingle correct
  6. 9 Apr 2024, Shift 1 · Q52A string is wrapped around the rim of a wheel of moment of inertia 0.40 kgm20.40\ \mathrm{kgm^2} and radius 1010 cm. The wheel is free to rotate…EasyNumerical value

Question text from the official JEE Main paper published by NTA; answer from the final answer key. Chapter, topic and idea tags, difficulty and skill are Lumi’s. This question needs a figure we do not reproduce; it is described in words above. Lumi analyses 42 of the 174 JEE Main shifts held from 2017 to 2026.